Micro-electromechanical system and method for production thereof

ABSTRACT

A micro-electromechanical system comprises a substrate (S) and at least two micro-elements ( 1, 2 ) of which a first is bistably switchable. The micro-elements ( 1, 2 ) have faces ( 3   a,    4   a ) facing one another, which are produced by a structuring method and thereby initially have at least one minimal distance from one another characteristic of the structuring method. The first micro-element ( 1 ) is then switched to the other stable state (B) whereby the distance between the faces ( 3   a,    4   a ) facing one another is smaller than the characteristic minimal distance for the structuring method. The micro-electromechanical system can be constructed as an electrostatically actuatable microswitch with improved switchability. Laterally and horizontally operating micro-electromechanical systems with new functionality and current-free closed relays can be implemented.

TECHNICAL FIELD

The invention relates to the field of micro-electromechanical systems,especially

-   -   to a micro-electromechanical system according to the preamble of        claim 1 and    -   to a method for manufacturing such a micro-electromechanical        system according to the preamble of claim 21.

PRIOR ART

Such a micro-electromechanical system (MEMS) forming the preamble ofclaims 1 and 21 and a corresponding method are known, for example, fromDE 198 00 189 A1. A micromechanical switch is described there, whichcomprises a flat support substrate, a contact piece positioned on thesupport substrate, a mobile electrode and a counter-electrode fixedlyconnected to the support substrate. The mobile electrode has a free endand a fixed end connected to the support substrate. The mobile electrodeand the counter-electrode have surfaces facing one another. By means ofelectrostatic forces of attraction between these mutually facingsurfaces, the mobile electrode can be bent, that is elasticallydeformed, such that the free end of the mobile electrode approaches thecounter-electrode and thereby also the contact piece until contactoccurs between the free end of the mobile electrode and the contactpiece. The movement of the free end of the mobile electrode in this casetakes place laterally, that is parallel to the flat support substrate.

The electrostatic forces of attraction between the mutually facingsurfaces of the mobile electrode and the counter-electrode are producedby applying a voltage between the mobile electrode and thecounter-electrode. In order to avoid a short circuit between the mobileelectrode and the counter-electrode, stoppers are inserted in thecounter-electrode which project over the surface of thecounter-electrode facing the mobile electrode and do not lie at the samepotential as the counter-electrode. For the same purpose, springs canalso be provided, which are attached to the side of the mobile electrodefacing away from the counter-electrode and restrict the movement of themobile electrode in the direction of the counter-electrode. In addition,for the same purpose, the surface of the mobile electrode facing thecounter-electrode can also be provided with an electrically insulatinglayer.

The electrostatic force of attraction F between two parallel surfaces ofarea A at the distance d on application of a switching voltage U betweenthe two surfaces is given byF=ε ₀ ·A·U ²(2d ²)

The force thus increases linearly with the area, quadratically with thevoltage and inversely proportional to the square of the distance.

The microsystem disclosed in said DE 198 00 189 A1 was produced using asilicon deep etching process on the support substrate. In this case, byapplying a mask to said support substrate, material is etched out fromthe support substrate at the points where the mask is open. Grooves oretching channels which at least have a characteristic minimal width forthe etching process are thereby formed.

In order to achieve mobility of the free end of the mobile electrode, asacrificial layer process is used which separates the free end of themobile electrode from the support substrate. For this purpose, asacrificial layer arranged in the support substrate below the mobileparts of the micromechanical switch is selectively removed by an etchingprocess, wherein the sacrificial layer continues to exist at points atwhich a connection to the substrate is desired such as at thecounter-electrode, the fixed contact piece and the fixed end of themobile electrode.

DE 42 05 029 C1 discloses an electrostatically operatedmicro-electromechanical relay which operates horizontally. That is, theswitching movement of this relay runs substantially perpendicular to asupport substrate. A tongue-shaped electrode with contact piece isfreely etched from a silicon substrate. The substrate is then applied toa counter-substrate with a counter-electrode and a counter-contact suchthat the electrode forms a wedge-shaped gap with the counter-electrode.By applying a switching voltage between the electrode and thecounter-electrode, these are movable towards one another whereby anelectrically conducting connection can be achieved between contact andcounter-contact. High contact forces can be achieved by relatively wideelectrodes.

DE 197 36 674 C1 also discloses a horizontally-operatingmicro-electromechanical relay and a method for its production. A movablecontact is attached to an anchor tongue affixed to one side of asubstrate, which is curved away from the substrate in the rest state. Inorder to produce a high contact force, this contact interacts with afixed contact which is also secured to a spring tongue curved away fromthe substrate. The curvature of the contact is achieved by applying atensile-stress layer to both contacts. In terms of productiontechnology, it is not easy to achieve a high reproducibility of acurvature of the contacts thus produced and therefore of the contactspacings in the rest state (opened).

U.S. Pat. No. 5,638,946 and U.S. Pat. No. 6,057,520 describe furtherhorizontally operating MEMS switches.

J. Qiu et al., “A Centrally-Clamped Parallel-Beam Bistable MEMSMechanism”, Proc. of MEMS 2001, Interlaken Switzerland, Jan. 20-22, 2001discloses a bistably switchable micro-electromechanical mechanism. Thisconsists of two parallel spring tongues or membranes suspended on bothsides, which describe a cosinusoidal profile. At the centre the springtongues are interconnected and at their ends they are fixed on a supportsubstrate. This bistable micro-element is produced by means of ionetching and sacrificial layer technology from the silicon supportsubstrate so that the spring tongues are movable laterally and twostable states are displayed. By applying a force directed perpendicularto the spring tongues and parallel to the support substrate, thebistable mechanism can be switched to and fro between the two bistablestates wherein the respective end position which is a mirror image ofthe initial position is finally achieved independently by snapping themechanism. In order to achieve elastic mobility on the one hand andmechanical stability of the micro-element on the other, the 3 mm longspring tongues are only 10 μm to 20 μm wide but 480 μm high.

Further laterally movable micro-electromechanical mechanisms aredescribed in M. Taher, A. Saif, “On a Tunable Bistable MEMS—Theory andExperiment”, Journal of Microelectromechanical Systems, Vol. 9, 157-170(June 2000).

U.S. Pat. No. 5,677,823 discloses a horizontally-operatingelectrostatically switchable bistable memory element. A bridge-likemovable contact aligned substantially parallel to a support substrate isarranged above a fixed contact fixedly connected to the supportsubstrate. The movable contact is fixed to the support substrate at bothits ends whereas at its centre it is arched away from the supportsubstrate (first stable position) or arched towards the supportsubstrate (second stable position). In the second stable position themovable contact and the fixed contact are in contact: the switch isclosed. In the first stable position the switch is opened. Thebistability of the switch is obtained by mechanical stresses which areincorporated into the movable contact during manufacture of the switch.Two electrodes are also arranged laterally next to the fixed contactbelow the movable contact. By applying electrical voltages to themovable contact and to these electrodes, contact and electrodes can beelectrically charged so that electrostatic forces of attraction orrepulsion are produced between them by which means the switch can beswitched to and fro between the two stable positions.

Another horizontally operating bistable MEMS mechanism is described inSun et al., “A Bistable Microrelay Based on Two-Segment MultimorphCantilever Actuators”, IEEE Catalog No. 98CH36176.

DESCRIPTION OF THE INVENTION

It is thus the object of the invention to provide amicro-electromechanical system (MEMS) of the type specified initiallywhich makes it possible to achieve a more flexible MEMS design. Inparticular, an improved switchability and new functionalities should bemade possible. This object is solved by an MEMS having the features ofclaim 1.

Furthermore, it is an object of the invention to provide an improvedmethod for MEMS manufacture. This object is solved by a method havingthe features of claim 21.

Improved switchability can, for example, mean that a switching processcan be triggered at lower switching voltages. New functionalities can,for example, mean realising voltageless closed connections ormicrorelays with both voltageless open and voltageless closedconnections.

The MEMS according to the invention comprises a substrate as well as afirst micro-element and a second micro-element, wherein

-   -   the first micro-element and the second micro-element are        connected to the substrate,    -   the first micro-element has a first face and the second        micro-element has a second face, which faces are facing one        another and are produced by a structuring process,    -   the first micro-element contains a switch section through which        it is bistably switchable between an initial position and a        working position and    -   the distance between the first face and the second face in the        working position of the first micro-element is shorter than a        minimal distance producible by the structuring method between        the first face and the second face.

Thus, a first micro-element switchable between the two stable positions,initial position and working position, is used in conjunction with asecond micro-element such that after switching from the initial positionto the working position, the first micro-element has a shorter distancefrom the second micro-element than in the initial position. Bothmicro-elements are connected to the substrate and produced using astructuring method. Said shorter distance in the working position is,according to the invention, shorter than a minimal distance between thetwo micro-elements characteristic of the structuring method.

In this way, it is achieved that new degrees of freedom are obtained inthe design of MEMS since boundary conditions pre-determined by theprocess technology are overcome. A wide range of micro-actuators can beimplemented anew or simply or in improved form.

In a preferred embodiment of the subject matter of the invention, thesecond micro-element has a first fixed end fixedly connected to thesubstrate and a movable part wherein in the working position of thefirst micro-element the movable part of the second micro-element ismovable by electrostatic forces between the first micro-element and thesecond micro-element from a switch-off position to a switch-on positionand wherein the two micro-elements have contact points in the area ofthe point at which said shorter distance between the two micro-elementsexists, and which are constructed as electrically non-conducting. Thefact that contact points exist means that said shorter distance is zero.

It is thus made possible to produce electrostatically operatingactuators whose electrostatically switchable electrodes (electrode andcounter-electrode) contact one another. The small or vanishing electrodegaps thereby achieved have an improved switchability in consequence. Itis possible to switch the actuator at very low switching voltages.

In a further advantageous embodiment of the subject matter of theinvention, the first micro-element is additionally constructed such thatit contains a matched counter-electrode which is matched to the shape ofthe second micro-element: the matched counter-electrode is shaped suchthat in the switch-on position of the second micro-element the matchedcounter-electrode and the second micro-element overlap over a large areain the area of said contact points. In the switch-on position of thesecond micro-element the matched counter-electrode and the secondmicro-element thus nestle up to one another. A maximisation of thesurfaces between which the electrostatic forces of attraction act isthereby achieved which results in higher electrostatic forces ofattraction and thus improved switchability. It is thus possible toswitch the actuator at very low switching voltages.

In a further advantageous embodiment said matched counter-electrodeadditionally comprises a second section which is set back in a stepshape with respect to the section of the counter-electrode nestling upto the second micro-element. In the switch-on position of the secondmicro-element, this second section of the matched counter-electrode andthe second micro-element enclose a gap. In this way, a force which thesecond micro-element can exert in its switch-on position can be tailoredand selected to be very large by suitably dimensioning the length, widthand height of the gap. The force which can be selected to be large inthis fashion can, for example, be a contact force of the secondmicro-element on one or two electric contacts which contact the secondmicro-element in its switch-on position whereby a more secure electricalcontact can be produced.

In a further preferred embodiment a changeover switch relay is achieved.

In other advantageous embodiments of the subject matter of theinvention, relays or changeover switch relays with voltageless closedconnections are realised.

In particular, in a preferred embodiment the movable part of the secondmicro-element is elastically deformable by switching the firstmicro-element from the initial position into the working position. It isthereby possible to achieve voltageless closed connections.

After the structuring of two micro-elements with mutually facing faces,the method according to the invention includes the switching over of thebistably switchable micro-element. New or improved MEMS such as thosespecified above can thereby be produced.

Further preferred embodiments are deduced from the dependent claims andthe figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the invention is explained in detail subsequentlywith reference to preferred embodiments which are shown in the appendeddrawings. In the figures:

FIG. 1 is a schematic diagram of an MEMS according to the invention witha cosinusoidal bistable element, in plan view;

FIG. 2 is a schematic diagram of an MEMS according to the invention withan antinode-shaped bistable element, in plan view;

FIG. 3 is a schematic diagram of an MEMS according to the invention witha cosinusoidal bistable element and matched counter-electrode, in planview;

FIG. 4 is a schematic diagram of a microrelay according to the inventionwith a cosinusoidal bistable element and matched counter-electrode, inplan view;

FIG. 5 is a schematic diagram of a micro-changeover switch relayaccording to the invention with two cosinusoidal bistable elements andmatched counter-electrode, in plan view;

FIG. 6 is a schematic diagram of a microrelay according to the inventionwith a cosinusoidal bistable element and stepped counter-electrode, inplan view;

FIG. 7 is a schematic diagram of a microrelay according to the inventionwith a cosinusoidal bistable element and stepped counter-electrode andtwo-part movable part of the second micro-element, in plan view;

FIG. 8 is a schematic diagram of a changeover switch relay according tothe invention with a monostable second micro-element and NO and NCconnections, in plan view;

FIG. 9 is a schematic diagram of a changeover switch relay according tothe invention with a bistable second micro-element and NO and NCconnections, in plan view;

FIG. 10 a is a schematic diagram of a microrelay according to theinvention with NC connection, state: first micro-element in initialposition; in plan view;

FIG. 10 b is a schematic diagram of a microrelay according to theinvention with NC connection, state: first micro-element in workingposition, second micro-element in switch-off position; in plan view;

FIG. 10 c is a schematic diagram of a microrelay according to theinvention with NC connection, state: first micro-element in workingposition, second micro-element in switch-on position; in plan view;

FIG. 11 a is a schematic diagram of a horizontally operating microrelayaccording to the invention with NC connection, cutaway side view;

FIG. 11 b is a schematic diagram of a horizontally operating microrelayaccording to the invention with NC connection, plan view;

The reference numbers used in the drawings and their meaning are listedin summarised form in the reference list. Basically, parts having thesame effect are provided with the same reference number in the figures.

WAYS FOR IMPLEMENTING THE INVENTION

FIG. 1 shows a schematic plan view of a first micro-electromechanicalsystem (MEMS) according to the invention. It comprises a firstmicro-element 1 and a second micro-element 2 which are both rigidlyconnected to a substrate S.

The substrate S is a wafer of single-crystal silicon where one of thetwo largest surfaces forms the principal surface of the substrate. InFIG. 1 this principal surface lies in the plane of the paper. The firstmicro-element 1 and the second micro-element 2 were formed from thesubstrate S by using deep ion etching (DRIE, dry reactive ion etching)and sacrificial layer technology.

The DRIE structuring method has the property of being amaterial-removing method; it is an etching method. It furthermore hasthe property of being well suited for producing narrow and deepchannels, gaps or grooves whereby a preferential direction can beallocated to the DRIE which specifies the direction of the preferredmaterial removal and thus lies perpendicular to the principal surface ofthe substrate. The width of a groove produced by means of DRIE isrestricted downwards, that is to narrow grooves, again perpendicular tothis preferential direction. This means that there is a minimumproducible groove width determined by the structuring method (forexample DRIE). For the two faces which form the lateral boundaries ofsuch a groove there is thus a minimal distance. Details of how themicro-elements 1,2 can be formed from the substrate by deep ion etchingand sacrificial layer technology are known to the person skilled in theart and can be obtained, for example, from said Unexamined Laid-OpenPatent Application DE 198 00 189 A1 which is hereby included with itstotal disclosure content in the description.

Micro-elements produced by DRIE typically have side faces aligned almostperpendicular to the principal surface of the substrate S or expresseddifferently: (local) surface normal vectors of the side faces run almostparallel to the principal surface of the substrate S. Suchmicro-elements thus substantially have the shape of a regular(rectangular) prism whose base surface is aligned parallel to theprincipal surface of the substrate S. In addition, the height of such amicro-element (perpendicular to the principal surface) is typically verylarge compared with the (narrowest) width of such a micro-element. Thefirst micro-element and the second micro-element are of this type.

The first micro-element 1 is constructed as a bistable elastic MEMSmechanism such as is described in said publication J. Qiu et al., “ACentrally-Clamped Parallel-Beam Bistable MEMS Mechanism”, Proc. of MEMS2001, Interlaken, Switzerland, Jan. 20-22, 2001. Details of embodiments,properties and on the manufacture of such a micro-element can beobtained from this publication which is hereby included in thedescription with its total disclosure content. The first micro-element 1is fixed at a first end 6 and a second end 7 on the substrate. Inbetween the first micro-element 1 has two parallel-runningcosinusoidally curved spring tongues which are interconnected at thecentre 8 between the two ends 6, 7. Considering their small width andtheir large height (perpendicular to the principal surface of thesubstrate), these spring tongues can also be considered to be parallelmembranes.

The first micro-element 1 is bistably switchable between an initialposition A and a working position B (the latter is shown dashed in FIG.1). That is, the micro-element 1 has two mechanically stable states orpositions A and B between which it can be moved to and fro underapplication of a lateral or substrate-parallel force; in this case, themovement takes place substantially laterally. Any intermediate positionsare not stable but independently result in a rapid transition to one ofthe two stable states A or B. The transition takes place by preferablyelastic deformation of the first micro-element 1. Here the firstmicro-element 1 thus merely consists of a switching section 5 by whichit is bistably switchable.

The first micro-element 1 has a side face formed by means of DRIE on theside facing the second micro-element 2, which is designated as firstface 3 a. This first face 3 a has a first coating 3 b which iselectrically insulating and whose outer surface 3, that is facing awayfrom the first face 3 a, forms the first surface 3 of the firstmicro-element 1. The first coating 3 b is typically produced byoxidation of the silicon.

The second micro-element 2 comprises a first fixed end 10 at which it isfixed on the substrate S and a movable part 11; it is arranged adjacentto the first micro-element 1. On that side of the second micro-elementfacing the first micro-element 1, the second micro-element 2 has a sideface formed by means of DRIE which is designated as second face 4 a.This second face 4 a has a second coating 4 b which is electricallyinsulating and whose outer surface, that is facing away from the secondface 4 a, forms the second surface 4 of the micro-element 2. The firstsurface 3 and the second surface 4 are mutually facing surfaces in thesame way that the first face 3 a and the second face 4 a are also facingone another. The second coating 4 b is also typically produced byoxidation of the silicon.

After forming the first face 3 a and the second face 4 a by means ofDRIE, the first micro-element 1 is located in the initial position A andthe second micro-element 2 in a switch-off position A′. Since the faces3 a and 4 a are formed by means of DRIE, they have a distance from oneanother which is at least as great as a minimal distance determined byDRIE. The distance of the faces from one another means the distancebetween two such points which lie closest to one another, wherein theone point lies on the first face 3 a and the other point lies on thesecond face 4 a. The distance is thus the width of the groove betweenthe first face 3 a and the second face 4 a at its narrowest point. InFIG. 1 this point is at a corner of the first fixed end 10 of the secondmicro-element 2 and close to the first end 6 of the first micro-element1 on the membrane of the first micro-element 1, which has the first face3 a.

The initial position A of the first micro-element 1 is an initialposition dependent on the manufacture. The arrangement of the firstmicro-element 1 and the second micro-element 2 is selected such thatafter switching the first micro-element 1 from the initial position Ainto the working position B, the distance of the first face 3 a from thesecond face 4 a is smaller than the said minimal distance determined bythe manufacturing method (for example, DRIE). In the MEMS in FIG. 1 thedistance is even zero, that is in the working position A the firstmicro-element 1 and the second micro-element 2 are in contact. In theworking position A an interaction of the first micro-element 1 with thesecond micro-element 2 can take place within the MEMS as prescribed.

The MEMS in FIG. 1 is a micro-actuator which is formed by the firstmicro-element 1 and the second micro-element 2 together with thesubstrate S. In this case, the second micro-element 2 acts as a movableelectrostatically switchable electrode and the bistably switchable firstmicro-element 1 acts as an electrostatic counter-electrode pertainingthereto. The first micro-element 1 is located in the working position A.

The mode of operation of the micro-actuator when it is in the workingposition B is substantially known from the prior art: a contactingelectrode C is provided at the first fixed end 6 of the firstmicro-element 1 and a contacting electrode C′ is provided at the firstfixed end 10 of the second micro-element 2. These contacting electrodesC, C′ are used to apply switching voltages to the micro-elements 1, 2 bywhich the micro-elements are electrostatically charged so thatelectrostatic forces act between the micro-elements 1 and 2. For thisthe material from which the micro-elements are made must be sufficientlyconductive which is achieved, for example, by suitably doping thesilicon. As a result of the electrostatic forces between themicro-elements (more accurately: between the first surface 3 and thesecond surface 4), the movable part 11 of the second micro-element 2 ismovable from the switch-off position A′ into the switch-on position B′of the second micro-element 2. The switch-on position B′ is shown dashedin FIG. 1. In the MEMS in FIG. 1 an opposite charging of themicro-elements 1, 2 and therefore an attracting electrostatic force isprovided. For switching the second micro-element 2 back into theswitch-off position A′ the charges of the micro-elements 1, 2 arereduced. The non-conducting coatings 3 b, 4 b ensure that no undesireddischarging takes place, especially when the micro-elements 1, 2 are incontact.

As can be deduced from Equation (1), the electrostatic force decreasesin inverse proportion to the distance. The MEMS according to theinvention from FIG. 1 thus has the major advantage of being switchableat lower switching voltages than would be required for an MEMS whosedistance between electrode and counter-electrode is greater than orequal to the minimal distance determined by the structuring method.

The micro-actuator in FIG. 1 can, for example, be used as an opticalmicro-switch wherein a light beam to be switched is transmitted orinterrupted by the movable part 11 of the micro-element 2 depending onwhether the second micro-element 2 is in the switch-off position A′ orin the switch-on position B′. Equally, it is also possible for a lightbeam to be deflected with the micro-actuator in FIG. 1, for example, ifa reflecting region (not shown) is arranged in the movable part 11 ofthe second micro-element 2. The switch-on position B′ is then present bydefinition when suitable switching voltages are applied; otherwise, theswitch-off position A′ is present.

The bistably switchable first micro-element 1 is used as anelectrostatic electrode or counter-electrode.

The embodiment in FIG. 1 was described in very great detail. For reasonsof clarity and lucidity, some of the details of the mode of operation ofthe MEMS according to the invention, which have already been mentionedand which should now have become clear to the person skilled in the art,are not specially mentioned again in the following.

FIG. 2 shows an MEMS which broadly corresponds to the MEMS from FIG. 1;however, the first micro-element 1 is differently constructed. Here thefirst micro-element 1 is constructed as another laterally, bistably andpreferably elastically switchable mechanism. Here also the firstmicro-element 1 is fixed at one first end 6 and one second end 7 on thesubstrates. In between however, the first micro-element 1 has a curvedspring tongue which has the shape of an antinode. Considering its smallwidth and its large height (perpendicular to the principal surface ofthe substrate) this spring tongue can also be designated as a membrane.

In the initial position A, that is in the state in which the firstmicro-element 1 is structured, the first micro-element 1 describes asymmetric antinode, in the working position B it describes an asymmetricantinode (the latter is shown dashed in FIG. 2). The asymmetric antinoderepresents the second stable position of the first micro-element 1 andcomes about by a stop fixedly connected to the substrate S contactingthe first micro-element 1 in the working position B and resulting incorresponding deformation of the first micro-element 1. This stop isformed here by a suitably constructed and arranged first fixed end 10 ofthe second micro-element 2. The corresponding contact point suitablylies to the right of the connecting section running from the second end7 to the first end 6 of the first micro-element 1 if the symmetricantinode is arranged in the initial position A to the left of thisconnecting section. The value of a position coordinate of the contactpoint drawn parallel to this connecting section is not 0.5 (noasymmetric antinode) and preferably lies between 0.52 and 0.92 of thelength of the connecting section; here it is about 0.84. The stop canalso be formed by a suitably shaped first end 6 or second end 7 of thefirst micro-element 1 or as a stop fixed separately on the substrate S(which should then be considered as belonging to the first micro-element1).

As in the embodiment from FIG. 1, the bistable micro-element 1 isproduced in the initial position A (structured), wherein the distancebetween the first micro-element 1 and the second micro-element 2 is atleast as large as a minimal distance (between these micro-elements 1, 2)determined by the structuring method. Still within the scope of themanufacture of the MEMS, after application of coatings 3 b, 4 b thefirst micro-element 1 is switched from the initial position A into theworking position B wherein in the working position B the distancebetween the two micro-elements 1, 2 is shorter than the said minimaldistance. Thus, two micro-elements are realised in the MEMS with a smalldistance from one another which cannot be produced by the structuringprocess (by using the bistable switchability of one of themicro-elements). For further details on the embodiment in FIG. 2,reference is made to that written in connection with FIG. 1.

FIG. 3 shows an MEMS according to the invention which broadlycorresponds to the exemplary embodiment shown in FIG. 1; however, thefirst micro-element 1 here not only comprises a switch section 5 butadditionally an electrode 9. The electrode 9 has an elongated sectionwhich contains the first face 3 a, the first coating 3 b and the firstsurface 3 of the first micro-element 1. This section is connected to theswitch section 5 at the centre 8 between the ends 6, 7 of the firstmicro-element 1 by means of a further elongated section which is alignedapproximately perpendicular to said section.

Since the electrode 9 is secured on the switch section 5, it moves withthe switch section 5 when switched from the initial position A to theworking position B (and back again if necessary). If electrostaticforces of attraction are produced between the first micro-element 1(naturally in the working position A) and the second micro-element 2 byapplying suitable switching voltages, the movable part 11 of the secondmicro-element 2 becomes elastically deformed and approaches theelectrode 9; it is switched from the switch-off position A′ to theswitch-on position B′. The shape of the electrode 9 and especially theshape of the first surface 3 is preferably formed such that the firstsurface 3 and the second surface 4 are in full-area contact in theswitch-on position. That is to say that there is areal contact betweenthe two surfaces 3, 4 which does not mean that the two surfaces 3, 4must be completely in contact. The first surface 3 is thus matched tothe shape of the second surface 4 in the switch-on position. The twosurfaces 3, 4 nestle up to one another in the switch-on position B′.Such an electrode 9 can be designated as a matched electrode 9. Theeffective area for the electrostatic forces is maximised and theeffective distances minimised by the matched electrode 9. Consequently,switching can be achieved at low switching voltage. For further detailson the embodiment in FIG. 3, reference is made to that written inconnection with FIG. 1.

FIG. 4 shows an MEMS which represents a micro-relay. The exemplaryembodiment broadly corresponds to that of FIG. 3. It also comprises a(matched) electrode 9 and a cosinusoidally constructed bistable elasticswitchable micro-element 1. In addition, the second micro-element 2, ormore accurately: the movable part 11 of the second micro-element 2, hasa contact region 16 which is electrically conductive. The contact region16 is preferably arranged in the area of that end of the movable part 11of the second micro-element 2 which does not border onto the first fixedend 10 of the second micro-element 2. The contact region 16 forms a partof a side face of the second micro-element 2 and is preferablyconstructed as a coating which is applied to the second micro-element 2by means of vapour deposition of sputtering techniques.

Furthermore, the MEMS comprises another two electrically conductivefixed contacts 17, 18 fixed on the substrate S. The arrangement of thefixed contacts 17, 18 and the contact region 16 is selected such that onapplication of suitable switching voltages to the first micro-element 1and the second micro-element 2 (that is in the switch-on position B′ ofthe second micro-element 2), the contact region 16 produces anelectrically conducting connection between the fixed contact 17 and thefixed contact 18. In the switch-off state A′ this is not the case. Thus,an electrostatic micro-relay is provided through which a connectionformed by the fixed contacts 17, 18 can be switched by means of theswitching voltages.

In this and also in the embodiments discussed further below, it is veryadvantageous that the distance in the open state between the contactregion 16 of the second micro-element 2 and the fixed contacts 17, 18can be selected and is highly reproducible in terms of productiontechnology.

In FIG. 4 the contact region 16 is arranged on that side of the secondmicro-element 2 which faces the first micro-element 1, that is on theside containing the surface 4. An electrical contact between the fixedcontacts 17, 18 can be accomplished by means of attractive electrostaticforces between the first micro-element 1 and the second micro-element 2.

It is also possible (not shown) to arrange the fixed contacts 17, 18such that they are located in that region of the substrate S which lieson the side of the second micro-element 2 facing away from the firstmicro-element 1. The contact region 16 is then accordingly arranged onthat side of the movable part 11 of the second micro-element 2 whichfaces away from the first micro-element 1. Constructed in this way, therelay can be switched by means of repelling electrostatic forces.Naturally, it is also possible to construct this micro-relay or themicro-relay shown in FIG. 4 with (matched) electrode 9 (similar to thestructure in FIG. 1).

FIG. 5 shows a micro-changeover switch relay. This contains all thefeatures of an MEMS such as that described in connection with FIG. 4. Inaddition however, the MEMS also has a third micro-element 1′ and twofurther fixed contacts 17′, 18′; and the second micro-element 2 has afurther electrically conductive contact region 16′ which is arranged onone side of the movable part 11 of the second micro-element 2 oppositeto the side having the contact region 16. The third micro-element 1′ andthe further fixed contacts 17′, 18′ are arranged as a mirror image tothe first micro-element 1 and the fixed contacts 17, 18 in relation tothe elongated movable part 11 of the second micro-element 2. Naturally,the arrangement need not be an exact mirror image; it is sufficient ifthe third micro-element 1′ is connected to the substrate in one area ofthe substrate S which lies on the side of the second micro-element (2)facing away from the first micro-element 1 and the further fixedcontacts 17′, 18′ are connected to the substrate in an area of thesubstrate S which lies on the side of the second micro-element 2 facingaway from the fixed contacts 17, 18. The structure of the thirdmicro-element 1′ corresponds to the structure of the first micro-element1. The further fixed contacts 17′, 18′ have the same type of structureas the fixed contacts 17, 18.

The interaction between the third micro-element 1′ and the secondmicro-element (2) and the further fixed contacts (17′, 18′) correspondsto the interaction between the first micro-element 1 and the secondmicro-element 2 and the fixed contacts 17, 18 described above. Onapplication of suitable switching voltages to the third micro-element 1′and the second micro-element 2, an electrically conducting connectioncan be made between the further fixed contacts 17′, 18′ by the furthercontact region 16′. Thus, this exemplary embodiment provides athree-position switch or a changeover switch relay which has threedefined states: (1.) contacts between both pairs of fixed contacts 17,18; 17′, 18′ open, (2.) contacts between the fixed contacts 17′, 18′open and contacts between the fixed contacts 17, 18 closed and (3.)contacts between the fixed contacts 17, 18 open and contacts between thefurther fixed contacts 17′, 18′ closed.

FIG. 6 shows a further MEMS according to the invention which broadlycorresponds to the MEMS from FIG. 4. It contains the features of theMEMS from FIG. 4 for which reference is made to the corresponding partof the description. However, the electrode 9 of the first micro-element1 is specially constructed here. The electrode 9 has an (opticallystep-shaped) recess. The electrode 9 comprises a gap-forming surface 12which is set back in a step shape with respect to the first surface 3 ofthe first micro-element 1. This electrode 9 can thus be designated as astepped electrode 9. In this MEMS attractive electrostatic forces areused for switching from the switch-off position A′ to the switch-onposition B′. If the first micro-element 1 is located in the workingposition B and the second micro-element 2 is located in the switch-onposition B′, the gap-forming surface 12 and the second micro-element 2or more accurately, the movable part 11 of the second micro-element 2,enclose a gap 13. The magnitude of a contact force exerted by the secondmicro-element 2 on the fixed contacts 17, 18 can thereby be selected. Inparticular, a very good, secure contact and a large contact force canthereby be achieved. The choice of the geometry of the gap allows aspecific pre-determination and choice of contact force. In particular,for this purpose the length of the gap and the width of the gap (that isthe distance between movable part 11 of the second micro-element 2 andthe gap-forming surface 12) and if necessary the profile of the gapwidth can be selected. Typically the length of the gap is about oneorder of magnitude, preferably about two orders of magnitude greaterthan the width of the gap. Advantageously, an (approximately) uniformlywide gap is selected and the first surface 3 contacts the second surface4 over the full area. The relative arrangement of the micro-elements 1,2 and the fixed contacts 17, 18 on the substrate should be madecarefully.

Furthermore, such an MEMS has the advantage that any problems withswitching from the switch-on position B′ to the switch-off position A′which may arise from slow or poor release of the movable part 11 of thesecond micro-element 2 from the electrode 9 (that is more accurately:from the first surface 3) as a result of surface effects, for example,can be reduced. The (air) gap 13 allows rapid release of the movablepart 11 of the second micro-element 2 from the electrode 9 whenswitching from the switch-on position B′ to the switch-off position A′whilst despite this, in the switch-on position B′ large electrostaticforces of attraction act between the first micro-element 1 and thesecond micro-element 2 if the gap width was selected as suitably small.

FIG. 7 shows a further advantageous embodiment of the invention. Thislargely corresponds to the embodiment shown in FIG. 6 and is describedon the basis of this. The movable part 11 of the second micro-element 2is specially constructed here. This has a first region 14 and a secondregion 15 wherein the first region 14 is constructed as less rigid, thatis more easily deformable than the second region 15. And the firstregion is arranged between the fixed first end 10 of the secondmicro-element 2 and the second region 15. The contact region 16 isadvantageously arranged in the second region 15, especially in the areaof the end of the second region 16 opposite the first region 15. Thesecond region 15 preferably comprises at least that region of themovable part 11 in which the movable part 11 and the secondmicro-element 2 are not opposite. Particularly advantageous is a (small)overlap of the second region 15 with the region of the movable part 11in which the movable part 11 and the second micro-element 2 areopposite. In the exemplary embodiment with stepped electrode 9 shown inFIG. 7, the second region 15 advantageously at least also comprises thatregion of the movable part 11 in which the movable part 11 and thegap-forming surface 12 are opposite. It is especially advantageous inthis case if the second region 15 also has a (small) overlap with thefirst surface 3. Advantageously in the switch-on state B′ full-surfacecontact takes place between the first surface 3 and a part of the secondsurface 4, this part of the second surface 4 lying completely within thefirst region 14.

The greater stiffness of the second region 15 compared to the firstregion 14 is achieved in the exemplary embodiment from FIG. 7 by thesecond region 15 being constructed as thicker or wider than the firstregion 14. It is also possible to make the second region 15 moredifficult to bend, for example, by applying a coating there; forexample, on a base surface of the regular prismatic body forming theregion 15 or on at least one of the side surfaces. This could beachieved by means of a suitably (large, long) constructed contact regionconstructed as a coating.

As a result of the differently stiff regions 14, 15, it is possible toswitch the second micro-element 2 from the switch-off position A′ to theswitch-on position B′ at low switching voltages and forces of attractionbetween the two micro-elements 1, 2; the movable part 11 (moreaccurately: the first region 14) of the second micro-element 2 nestlesup to the electrode 9, by unrolling, even at low forces of attraction onthe electrode 9. This is whilst in the second region and preferably inthe contact region 16, no- or only slight deformation of the secondmicro-element 2 is to be expected. In this way, a secure electricalcontact can be produced between the fixed contacts 17, 18 by means ofthe contact region 16.

Said features can naturally also be applied to the exemplary embodimentsdescribed further above and further below (FIG. 1 to FIG. 6 and FIG. 8to FIG. 11 b).

FIG. 8 shows a further advantageous embodiment of the invention, namelya changeover switch relay which, in addition to a normally-openconnection (NO connection) also comprises a normally-closed connection(NC connection). NO connection means that in the event ofnon-application of a suitable switching voltage, the connection is open(voltageless open), as is the case in the exemplary embodimentsdescribed above (FIG. 4 to FIG. 7). NC connections which are closed inthe event of non-application of a suitable switching voltage(voltageless closed) are difficult to achieve on the other hand but areachieved in this embodiment. In particular, an NC connection in an MEMSstructured by means of DRIE is achieved here.

The MEMS in FIG. 8 has a mirror-image structure and comprises a firstmicro-element 1, a third micro-element 1′, a fourth micro-element 19 anda fifth micro-element 20 which are all bistably switchable and have astable initial position A (shown by the continuous line) and a stableworking position B (shown by the dashed line). They are constructed hereas bistable micro-elements such as those described more accurately inconnection with FIG. 1 (two parallel, cosinusoidal spring tonguesconnected at their centre). The position in which these micro-elementsare structured using DRIE is the initial position A. The firstmicro-element 1 and the third micro-element 1′ broadly correspond to oneanother in their function. They merely consist of one switch section 5.The fourth micro-element 19 and the fifth micro-element 20 also largelycorrespond to one another in their function. They each have onecontacting electrode D, D′ (for applying a signal to be switched, forexample, an electric current) and an electrically conductive contactelectrode 21, 22. The conductivity of the contact electrodes 21, 22 ispreferably produced by a metal coating. The contact electrodes 21, 22are constructed as elongated, finger-shaped and fixed to the respectivemicro-element 19, 20 approximately at the centre 8 between the two endsof the respective micro-element 19, 20. Furthermore, the MEMS hasanother two fixed electrodes 17, 18 fixedly connected to the substrate S(for application of a further electric current to be switched).

The MEMS in FIG. 8 furthermore comprises a second micro-element 2. Thesecond micro-element 2 is a monostably switchable micro-element; it hasonly one stable position. It comprises a first fixed end 10 and a secondfixed end 10′ which ends 10, 10′ are fixed on the substrate S, and amovable part 11 arranged between these two fixed ends 10, 10′. Themovable part 11 is constructed as a bent, preferably antinode-shapedstructure which is secured to the two fixed ends 10, 10′ of the secondmicro-element 2 and has an electrically conductive contact region 16.The movable part 11 furthermore has a second surface 4 which is formedby an optional second coating 4 b and which second surface 4 faces afirst surface 3 of the first micro-element 1. A fourth surface 4′ of thesecond micro-element 2 and a third surface 3′ of the third micro-element1′ are in a similar relationship. The second surface 4 is arrangedbetween the first fixed end 10 and the contact region 16. Similarly, thefourth surface 4′ is arranged between the second fixed end 10′ and thecontact region 16. After the structuring of the second micro-element 2,the movable part 11 is located in the switch-off position A′, the stableposition of the second micro-element 2.

As a result of the existence of the minimal distance already mentionedabove between two micro-elements or surfaces produced by means of DRIE,the bistable micro-elements 1, 1′, 19, 20 are separated from the secondmicro-element 2 by at least such a minimal distance. After applying theoptional non-conducting coatings 3 b, 3 b′ of the first or thirdmicro-elements 1, 1′ and the optional electrically conductive coatingsof the contact electrodes 21, 22, the bistable micro-elements 1, 1′, 19,20 are switched from the initial position A to the working position B aspart of the method of manufacturing the MEMS according to the invention.As a result, the distance between the micro-elements or surfaces isshorter than said minimal distance; in FIG. 8 the micro-elements areeven in contact. In particular, two contact electrodes 21, 22 are incontact with the contact region 16. An electrically conductingconnection is thereby produced between the two contact electrodes 21, 22and thus the NC connection. In this way, a voltageless closed butreleasable contact is achieved. The surfaces 3, 4 and the surfaces 3′,4′ are respectively also in contact. As a result, by applying relativelylow switching voltages between the second micro-element 2 and the firstmicro-element 1 and between the second micro-element 2 and the thirdmicro-element 1′, sufficiently large electrostatic forces of attractioncan thereby be produced between the second micro-element 2 and themicro-elements 1, 1′ which result in switching of the secondmicro-element 2 from the switch-off position A′ to the switch-onposition B′. In the switch-on position B′ the NC connection is now openwhereas the NO connection is closed. As a result of its monostability,the second micro-element 2 switches itself back into the switch-offposition in the event of non-application of a suitable switchingvoltage: NC connection closed, NO connection open.

Numerous modifications of the embodiment in FIG. 8 are feasible andadvantageous: here are some examples:

-   -   It is possible to construct the MEMS so that it is not        mirror-symmetrical.    -   The fixed contacts 17, 18 can be dispensed with and an        NC-connection micro-relay is then obtained.    -   The micro-elements 19, 20 can be dispensed with and an        NO-connection micro-relay is then obtained.    -   If the fixed contacts 17, 18 or the micro-elements 19, 20 are        dispensed with, it is sufficient if the contact region 16 of the        second micro-element 2 is only electrically conductive on one        side.    -   The micro-elements 1, 1′ can be provided with (matched,        optionally stepped) electrodes 9 (see FIG. 3 to FIG. 7).    -   The contacting electrodes 21, 22 can be constructed differently;        or they can be dispensed with completely and contact is then        made with the contact section 16 of the second micro-element 2        by means of the preferably electrically conductive coated switch        section.    -   It is possible to arrange the micro-elements 1, 1′ on the other        side of the second micro-element 2, that is in the area of the        substrate S which lies on the side of the second micro-element 2        facing away from the fixed contacts 17, 18. The micro-relay is        then switchable by electrostatic repelling forces.    -   It is also possible to arrange the first micro-element 1 in a        different region (of the substrate S, in relation to the second        micro-element 2) compared to the third micro-element 1′.    -   The third micro-element 1′ can be dispensed with and only the        first micro-element 1 can be used as electrostatic        counter-electrode to the second micro-element 2 as movable        electrode.

Said features can be advantageous jointly or individually or in anycombination.

FIG. 9 shows a changeover switch relay which in addition to a normallyopen connection (NO connection) additionally comprises a normally closedconnection (NC connection). The MEMS has a structure very similar tothat described in FIG. 8; for corresponding features reference is madeto the above text. However, the second micro-element 2 is not monostablebut bistable here. In particular, it has a structure with two parallel,cosinusoidal spring tongues connected at their centre as is described indetail in connection with FIG. 1. The two stable positions of the secondmicro-element 2 are the switch-off position A′ and the switch-onposition B′. A major advantage of the bistability of the secondmicro-element 2 is that it requires no applied switching voltage to keepthe second micro-element 2 in the switch-off position A′ or theswitch-on position B′. After applying a suitable switching voltage andthe switching process to the other state A′, B′ thereby induced, thesecond micro-element 2 independently remains in this state A′, B′. As aresult, each of the two pairs of contacts to which a signal to beswitched is applied (fixed electrodes 17, 18 or micro-element 19, 20)can be an NO connection or an NC connection.

In addition, the MEMS in FIG. 9 has two further bistably switchablemicro-elements: the sixth micro-element 23 and the seventh micro-element24. These are also constructed here with two parallel cosinusoidalspring tongues connected at their centre and each have a (matched)electrode 9. They are arranged in the area of the substrate S which lieson that side of the second micro-element 2 facing the micro-elements 1,1′. The micro-elements 23, 24 interact with the micro-element 2 in asimilar fashion to the micro-elements 1, 1′. For example, for thispurpose the second micro-element 2 has a sixth face 26 a and an eighthface 26 a′ which interact with a fifth face 25 a (of the sixthmicro-element 23) or a seventh face 25 a′ (of the seventh micro-element24). By means of electrostatic forces of attraction between the secondmicro-element 2 and the sixth micro-element 23 (more accurately: betweenthe corresponding faces or surfaces) or the seventh micro-element 24(more accurately: between the corresponding faces or surfaces), thesecond micro-element 2 can be switched from the switch-on state B′ tothe switch-off state A′.

A plurality of advantageous modifications of this embodiment arefeasible:

-   -   It is possible that the MEMS does not have a mirror-symmetrical        structure.    -   The fixed contacts 17, 18 can be dispensed with.    -   The micro-elements 19, 20 can be dispensed with.    -   If the fixed contacts 17, 18 or the micro-elements 19, 20 are        dispensed with, it is sufficient if the contact region 16 of the        second micro-element 2 is only electrically conductive on one        side.    -   The micro-elements 1, 1′ can be provided with (matched,        optionally stepped) electrodes 9 (see FIG. 3 to FIG. 7).    -   The micro-elements 23, 24 can be used without matched electrodes        9.    -   The contacting electrodes of the micro-elements 19, 20 can be        constructed differently; or they can be completely dispensed        with and then contact the contact section 16 of the second        micro-element 2 by means of the preferably electrically        conductive coated switch section.    -   It is possible to switch the micro-relay by electrostatic        repulsive forces; or to switch it by means of electrostatic        repulsive forces and electrostatic attractive forces.    -   One, two, or three of the micro-elements 1, 1′, 23, 24 can be        dispensed with; in particular the micro-elements 1, 24 or the        micro-elements 1′, 23 located diagonally opposite to one        another.    -   If a switching process is produced by interaction of at least        two micro-elements 1, 1′, 23, 24 with the second micro-element        2, it is especially advantageous if at least one of the        corresponding switching voltages is applied with a time delay        relative to at least one of the other switching voltages. The        movement that the movable part 11 of the second micro-element 2        makes during the switching process can thereby be supported. In        particular, the asymmetric movement of the two parallel,        cosinusoidally curved spring tongues of the second micro-element        2 can be taken into account. Suitably matched time switching        voltage profiles can also be used.    -   If instead of a cosinusoidal bistable second micro-element 2, an        antinode-shaped micro-element is used, the fixed contacts 17, 18        or the fourth and/or fifth micro-element 19, 20 are        advantageously arranged such that at least one of these provides        for the asymmetric construction of the antinode.

Said features can be advantageous jointly or individually or in anycombination.

FIGS. 10 a to 10 c show a further advantageous embodiment of theinvention in various positions. This MEMS comprises a micro-relay withan NC connection which can generally only be achieved with difficulty.The MEMS is described starting from the exemplary embodiment in FIG. 4since this has the same components. FIG. 10 a shows the MEMS in thestate which it has after structuring by means of DRIE: the firstmicro-element 1 is located in the initial position A. FIG. 10 b showsthe MEMS in a state where the first micro-element 1 is located in theworking position B and the second micro-element 2 is in the switch-offstate A′. FIG. 10 c shows the MEMS in a state in which the firstmicro-element is in the working position B and the second micro-element2 is in the switch-on state B′.

Unlike the embodiments discussed further above, here it is the case thatafter switching over from the initial position A to the working positionB, the first micro-element 1 not only simply comes nearer to the secondmicro-element 2 than the minimal distance determined by DRIE and merely(lightly) contacts the second micro-element 2. Rather, the arrangementof the micro-elements 1, 2 on the substrate S and the configuration ofthe micro-elements 1, 2 is selected here such that the firstmicro-element 1 in the working position B exerts a force on the movablepart 11 of the second micro-element 2 which results in a (significant)elastic deformation of the movable part 11 of the second micro-element 2(see FIG. 10 b). The movable part 11 of the second micro-element 2 isdeformed such that the electrically conductive contact region 16 of thesecond micro-element 2 connects the fixed contacts 17, 18 in aconducting fashion: the NC connection is closed. A voltageless closedbut releasable contact is achieved in an MEMS structured using DRIE.Expressed differently: a switching process of the second micro-element 2is induced by the switching of the first micro-element 1 from theinitial position A to the working position B. Since no switching voltageneeds to be applied for this, after the switching process the secondmicro-element 2 is in the switch-off position A′. In order to open theNC connection again, a suitable switching voltage must be appliedbetween the first micro-element 1 and the second micro-element 2. The NCconnection is opened by means of electrostatic forces of attraction andthe second micro-element 2 goes into the switch-on state B′ (see FIG. 10c).

On the basis of FIGS. 10 a-10 c, further advantageous embodiments can becreated in combination with features specified further above. Inparticular, the electrode 9 can be dispensed with. Or the electrode 9can be constructed differently. In particular, the electrode 9 can beadvantageously constructed and the micro-elements 1, 2 arranged withrespect to one another such that the contact points between the twomicro-elements 1, 2 (when the first micro-element 1 is in the workingposition A and the second micro-element 2 is in the switch-off positionA′) lies substantially on a straight line with the centre 8 in theinitial position A and the centre 8 in the working position. A lowmechanical loading of the first micro-element 1 can thereby be achievedwherein at the same time large contact forces can be exerted on thefixed contacts 17, 18 (secure contacts).

It is also advantageous, by analogy with the embodiment shown in FIG. 5,to provide a second pair of fixed contacts 17′, 18′ (not shown in FIG.10) wherein these fixed contacts 17′, 18′ are to be arranged such thatthe contact region 16 of the second micro-element 2 interconnects thesefixed contacts 17′, 18′ in an electrically conducting fashion if thesecond micro-element 2 is located in the switch-on position B′. Achangeover switch relay is thus obtained, similar to that from FIG. 5but with only one bistable micro-element 1. The movable part 11 of thesecond micro-element 2 can advantageously also be constructed astwo-part (similar to the embodiment in FIG. 7).

Only laterally operating MEMS were discussed in the above embodiments.However, it is also possible to construct the MEMS described (in similarform) as horizontally operating MEMS. Then DRIE is not typically usedfor the manufacture but rather other methods known from MEMS orsemiconductor technology are used, such as those mentioned in theaforesaid patent specifications U.S. Pat. No. 5,638,946, U.S. Pat. No.5,677,823 or DE 42 05 029 C1. The disclosure content of these patentspecifications is thus hereby included in the present description.

FIGS. 11 a and 11 b show a possible exemplary embodiment in which themovable parts of the MEMS are substantially horizontally movable. FIG.11 a is cutaway side view of the MEMS shown in plan view in FIG. 11 b.In FIG. 11 b the line of the section in FIG. 11 a is indicated byXIa-XIa. The MEMS is a micro-relay with an NC connection.

The first micro-element 1 here is constructed as an antinode-shapedbistable elastically switchable micro-element similar to the firstmicro-element 1 shown in FIG. 2. In the initial position A the symmetricantinode is arched away from the substrate S. The second end 7 of thefirst micro-element 1 is constructed here as bridge-like. As a result,the second micro-element 2 arranged below the antinode can extend tooutside the region between the first end 6 and the second end 7 of thefirst micro-element 1. The first fixed end 10 of the secondmicro-element 2 is here used as a stop for the formation of theasymmetric antinode of the first micro-element 1 in the working positionB.

The movable part 11 of the second micro-element 2 initially (after thestructuring) runs substantially parallel to the principal surface of thesubstrate S. After switching the first micro-element 1 from the initialposition A into the working position B, the first micro-element 1 exertsa compressive force on the movable part 11 of the second micro-element2. The second micro-element 2 is elastically deformed. It enters intoits switch-off position A′ in which a movable contact electrode Efixedly attached to the movable part 11 contacts a fixed electrode 17fixed on the substrate S. An NC connection is thereby produced betweenthe movable contact electrode E and the fixed electrode 17. Thisproduction of an NC connection is quite similar to the method describedin connection with FIGS. 10 a to 10 c.

If suitable switching voltages are applied between the twomicro-elements 1, 2, the second micro-element 2 is transferred into theswitch-on state B′ in which the movable part 11 of the secondmicro-element 2 is bent away from the substrate and the NC connection isopen. The contacting electrodes C, C′ are used to apply switchingvoltages. Contacting electrodes D, D′ are used to apply a signal to beswitched. The contacting electrode D which is electrically connected tothe movable contact electrode E is arranged here on the first fixed end10 of the second micro-element 2. The contacting electrode D′electrically connected to the fixed contact 17 is arranged on thesubstrate S.

Other MEMS according to the invention, such as the MEMS describedfurther above can also be implemented as horizontally operating MEMS.

An arrangement with a fixed electrode 17 and a movable contact electrodeE, as in FIGS. 11 a and 11 b can also advantageously be implemented inthe MEMS described further above, which are described with a contactregion 16 and two fixed electrodes 17, 18.

In the embodiment from FIGS. 11 a, b it is very advantageous that thedistance in the open state between the movable contact electrode E ofthe second micro-element 2 and the fixed contact 17 can be selected andis highly reproducible in terms of production technology. The same alsoapplies to the embodiments discussed further above provided that theseare implemented similar to FIGS. 11 a, b with a movable contactelectrode E.

The MEMS according to the invention can not only be implemented asswitches or relays as in the above examples. A wide range ofmicro-actuators can be implemented. For example, MEMS according to theinvention can be micro-valves or micro-pumps or actuate such.

The substrate S used to manufacture the MEMS according to the inventionis preferably constructed as flat. It typically has a principal surfacewhich is structured to produce the MEMS, wherein the movement of themovable parts of the MEMS are movable substantially parallel orperpendicular to this principal surface. The substrate S preferablyconsists of a semiconductor material, especially silicon which isadvantageously single-crystal and especially advantageously (for asufficient electrical conductivity) is also doped. In the case ofsingle-crystal silicon, advantageously no- or only very slow, relaxationis to be expected for bistably switchable micro-elements 1, 1′, 2, 19,20, 23, 24 under mechanical stress.

In particular, an SOI (silicon-on-insulator) wafer can be usedconsisting of three substrate-parallel layers, silicon-siliconoxide-silicon. The silicon oxide layer is used as the sacrificial layer.

The structuring method mentioned is typically a material-removingmethod, preferably an etching method. The LIGA technique or especiallyreactive ion etching and especially advantageously deep ion etching(DRIE) can be considered here. The DRIE method has the advantage ofbeing very suitable for producing surfaces which (relative to theirheight perpendicular to the substrate) are closely spaced and run almostperpendicular to the principal surface of the substrate S. DRIE is wellsuited for the manufacture of laterally operating MEMS. However, methodswhich deposit material are also feasible, for example, if mutuallyfacing faces thus produced have a minimal spacing dependent on themethod. For example, there are rapid prototyping methods usingphotopolymerisation.

In addition to electrostatically actuatable actuators,electromagnetically or piezoelectrically actuatable actuators can alsobe implemented according to the invention. The actuating forces can berepulsive or attractive.

The bistably switchable micro-element according to the invention canalso be tristably or otherwise multistably switchable. In addition, forsome applications after the first switching from the initial position Ato the working position B it is not necessary for the micro-elements 1,1′, 19, 20, 23, 24 to be switchable back to the initial position A. Asingle, for example, plastic deformation can also be considered.However, the micro-elements 1, 1′, 19, 20, 23, 24 are preferablybistably elastically switchable and switchable back into the initialposition A. It is especially advantageous if the bistable micro-elements1, 1′, 2, 19, 20, 23, 24 are constructed as the cosinusoidal orantinode-shaped micro-elements described wherein these can also beimplemented in modified form and combined within an MEMS.

Depending on the purpose, the micro-elements can optionally haveelectrically conducting or electrically non-conducting coatings. Anon-conducting coating is preferably used to prevent discharges betweenelectrostatic electrodes in contact with one another. For example,stoppers or springs can be used as alternative or additional protectionfrom such discharges, as are known from DE 198 00 189 A1 already cited.The contacting electrodes C, C′, D, D′ can be produced in a knownfashion (for example, by sputtering) and can be contacted for example bybonding.

For the manufacturing process for the MEMS according to the invention itshould be noted that the first switching of the first micro-element 1and also the other bistably switchable micro-elements 1′, 19, 20, 23, 24from the initial position A to the working position B should beconsidered as still belonging to the MEMS manufacturing process. Thisinitial switching process can take place mechanically. Preferablyhowever this switching process is carried out as part of a quality orfunction test (burn-in) of the MEMS wherein other units connected to thesubstrate can be co-tested or initialised. The initial switching processcan then preferably take place by producing an attractive force betweenthe bistable micro-element 1, 1′, 19, 20, 23, 24 and the secondmicro-element 2, wherein this force advantageously takes place byapplying a switching voltage. Such a switching voltage is typicallyhigher than a switching voltage used to switch the second micro-element2 between switch-off position A′ and switch-on position B′.

Said features can be advantageous jointly or individually or in anycombination.

The linear expansion of the MEMS described is typically between 0.2 mmand 5 mm, preferably 0.8 mm to 2 mm. For DRIE as a structuring methodsaid minimal distance (minimal groove width) is about 5 μm to 15 μm; ithas a typical dependence on the depth of the structured groove. Thedepth of the structured groove is typically 300 μm to 550 μm. Byswitching from the initial position A to the working position B, thecorresponding distance is reduced to typically zero or 0.1 μm to 1 μm.Layer thicknesses of the non-conducting coatings 3 b, 3 b′, 4 b. 4 b′are typically 50 nm to 500 μm.

The switching voltages for the MEMS described (switching betweenswitch-off position A′ and switch-on position B′) are typically 10 V to80 V, preferably 25 V to 50 V. When the first switching of the bistablemicro-elements from the initial position A to the working position takesplace by electrostatic forces of attraction, switching voltages between70 V and 300 V, preferably between 100 V and 200 V are used for this.

REFERENCE LIST

-   1 First micro-element-   1′ Third micro-element-   2 Second micro-element-   3 First surface (of the first micro-element);-   3 a facing the second surface-   3 a First face (of the first micro-element); facing the second face-   3 b First coating (of the first face)-   3′ Third surface (of the third micro-element); facing the fourth    surface-   3 a′ Third face (of the third micro-element); facing the fourth face-   3 b′ Third coating (of the third face)-   4 Second surface (of the second micro-element); facing the first    surface-   4 a Second face (of the second micro-element); facing the first face-   4 b Second coating (of the second face)-   4′ Fourth surface (of the second micro-element); facing the third    surface-   4 a′ Fourth face (of the second micro-element); facing the third    face-   4 b′ Fourth coating (of the fourth face)-   5 Switch section of the first micro-element-   6 First end of the first micro-element-   7 Second end of the first micro-element-   8 Centre between the first and the second end of the first    micro-element-   9 (Matched) electrode of the first micro-element-   10 First fixed end of the second micro-element-   10′ Second fixed end of the second micro-element-   11 Movable part of the second micro-element-   12 Gap-forming surface-   13 Gap-   14 First region of the movable part of the second micro-element-   15 Second region of the movable part of the second micro-element-   16,16′ Contact region of the movable part of the second    micro-element-   17,18 Fixed contacts-   17′,18′ Fixed contacts-   19 Fourth micro-element-   20 Fifth micro-element-   21,22 Contact electrodes-   23 Sixth micro-element-   24 Seventh micro-element-   25 a Fifth face (of the sixth micro-element); facing the sixth face-   25 a′ Seventh face (of the seventh micro-element); facing the eighth    face-   26 a Sixth face (of the second micro-element); facing the fifth face-   26 a′ Eighth face (of the second micro-element); facing the fifth    face-   A Initial position-   B Working position-   A′ Switch-off position (of the second micro-element)-   B′ Switch-on position (of the second micro-element)-   C,C′ Contacting electrodes-   D,D′ Contacting electrodes-   E Movable contacting electrodes (of the second micro-element)-   S Substrate

1. A micro-electromechanical system, comprising a substrate as well as afirst micro-element and a second micro-element, wherein (a) the firstmicro-element and the second micro-element are connected to thesubstrate and (b) the first micro-element has a first face and thesecond micro-element has a second face, which faces face one another andare produced by a structuring method, wherein (d) the firstmicro-element contains a switch section by which it is bistablyswitchable between an initial position and a working position, and (e)the distance between the first face and the second surface in theworking position of the first micro-element is smaller than a minimaldistance producible by the structuring method between the first face andthe second face.
 2. The micro-electromechanical system according toclaim 1, wherein (a) the first micro-element has a first surface whichis the same as the first face or, if the first face is provided with afirst coating, is the same as the surface of this coating and (b) thesecond micro-element has a second surface which is the same as thesecond face or, if the second face is provided with a second coating, isthe same as the surface of this coating.
 3. The micro-electromechanicalsystem according to claim 2, wherein (a) the second micro-element has afirst fixed end fixedly connected to the substrate and a movable part,wherein (b) the first surface and the second surface are electricallynon-conducting and (c) the first surface and the second surface havecontact points in the working position and (d) the second micro-elementis thereby switchable from a switch-off position to a switch-onposition, that in the working position of the first micro-element themovable part of the second micro-element is movable by electrostaticforces between the first micro-element and the second micro-element. 4.The micro-electromechanical system according to claim 3, wherein (a) thefirst micro-element comprises an electrode, which electrode contains thefirst surface and (b) the electrode and the second micro-element areconstructed such that in the switch-on position of the secondmicro-element the first surface and the second surface are in full-areacontact.
 5. The micro-electromechanical system according to claim 4,wherein the electrode has a gap-forming surface which is constructedsuch that it is set back in a step fashion with respect to the firstsurface and with the second micro-element encloses a gap when the firstmicro-element is in the working position and the second micro-element isin the switch-on position.
 6. The micro-electromechanical systemaccording to claim 3, wherein the movable part of the secondmicro-element has a first region and a second region, wherein the firstregion is arranged between the second region and the first fixed end ofthe second micro-element, comprises a part of the second surface and isconstructed as less stiff than the second region.
 7. Themicro-electromechanical system according to claim 3, wherein (a) themicro-electromechanical system has two fixed contacts fixedly connectedto the substrate, and (b) the movable part of the second micro-elementhas an electrically conductive contact region, which contact region isarranged in the area of the end of the second micro-element opposite tothe first fixed end of the second micro-element, and through whichcontact region in the switch-on position of the second micro-element thetwo fixed contacts are interconnected in a conducting fashion.
 8. Themicro-electromechanical system according to claim 7, wherein (a) themicro-electromechanical system comprises a third micro-element which isbistably switchable, which is connected to the substrate and which isarranged in a region which lies on the side of the second micro-elementfacing away from the first micro-element and (b) that themicro-electromechanical system has two further fixed contacts whichfurther fixed contacts are fixedly connected to the substrate and arearranged in a region which lies on the side of the second microelementfacing away from the fixed contacts, (c) that the movable part of thesecond micro-element has a further electrically conductive contactregion which is arranged in the area of an end of the secondmicro-element opposite to the first fixed end of the secondmicro-element, on the side of the second micro-element facing away fromthe contact region, and (d) wherein the third micro-element interactswith the second micro-element and with the further fixed contacts in afashion similar to that in which the first micro-element interacts withthe second micro-element and with the fixed contacts.
 9. Themicro-electromechanical system according to claim 6 wherein the contactregion is arranged in the second region of the movable part of thesecond micro-element.
 10. The micro-electromechanical system accordingto claim 1, wherein (a) the micro-electromechanical system comprises athird micro-element which is connected to the substrate and has a thirdface, (b) the second micro-element contains a switch section which has afirst fixed end fixedly connected to the substrate, a second fixed endfixedly connected to the substrate, a movable part arranged betweenthese two fixed ends and a fourth face and (c) through which switchsection the second micro-element is switchable between a switch-offposition and a switch-on position, wherein (d) the movable part of thesecond micro-element comprises an electrically conductive contactregion, (e) the second face is arranged between the first fixed end andthe contact region, and (f) the fourth face is arranged between thesecond fixed end and the contact region, (g) the third face and thefourth face are produced by the structuring method and are facing oneanother, and (h) the third micro-element contains a switch sectionthrough which it is bistably switchable between an initial position anda working position, and (i) the distance between the third surface andthe fourth face in the working position of the third micro-element issmaller than a minimal distance producible by the structuring methodbetween the third face and the fourth face.
 11. Themicro-electromechanical system according to claim 10, wherein (a) thethird micro-element has a third surface which is the same as the thirdface or, if the third face is provided with a third coating, is the sameas the surface of this coating, and (b) the second micro-element has afourth face which is the same as the fourth face or, if the fourth faceis provided with a fourth coating, is the same as the surface of thiscoating.
 12. The micro-electromechanical system according to claim 11,wherein (a) the micro-electromechanical system contains two fixedcontacts fixedly connected to the substrate, (b) the secondmicro-element is thereby switchable from its initial position into itsswitch-on position, that in the working position of the firstmicro-element and of the third micro-element the movable part of thesecond micro-element is elastically movable by electrostatic forcesbetween the first microelement and the second micro-element and betweenthe third micro-element and the second micro-element, and (c) in theswitch-on position of the second micro-element the two fixed contactsare interconnected by the contact region in a conducting fashion. 13.The micro-electromechanical system according to claim 12, wherein (a)the micro-electromechanical system comprises a fourth micro-element anda fifth micro-element (b) which micro-elements are connected to thesubstrate in an area which lies on the side of the second micro-elementfacing away from the fixed contacts, contains switch sections throughwhich they are bistably switchable between an initial position and aworking position, and which each have a contact electrode provided withan electrically conductive coating, and (c) in the switch-off positionof the second micro-element in the working position of the fourthmicroelement and the fifth micro-element the two contact electrodes areinterconnected by the contact region in an electrically conductingfashion.
 14. The micro-electromechanical system according to claim 10,wherein the second micro-element is bistably elastically switchablebetween its initial position and its switch-on position.
 15. Themicro-electromechanical system according to claim 14, wherein (a) themicro-electromechanical system comprises a sixth micro-element and aseventh micro-element, (b) which micro-elements are connected to thesubstrate, are arranged on the side of the second micro-element which isfacing away from the second surface and the fourth surface, containswitch sections through which they are bistably switchable between aninitial position (A) and a working position, (c) the sixth micro-elementhas a fifth face, (d) the second micro-element has a sixth face which isarranged on the side of the second micro-element facing away from thesecond surface between the first fixed end and the contact region, (e)the fifth face and the sixth face are facing one another and areproduced by the structuring method, (f) the seventh micro-element has aseventh face, (g) the second micro-element has an eighth face which isarranged on the side of the second micro-element facing away from thefourth surface between the second fixed end and the contact region, (h)the seventh face and the eighth face are facing one another and producedby the structuring method, and (i) the distance between the fifth faceand the sixth face in the working position of the sixth micro-element issmaller than a minimal distance producible by the structuring methodbetween the fifth face and the sixth face, and (i) the distance betweenthe seventh face and the eighth face in the working position of theseventh micro-element is smaller than a minimal distance producible bythe structuring method between the seventh face and the eighth face and(j) the second micro-element is thereby switchable from its switch-onposition into its switch-off position, that in the working position ofthe sixth micro-element and the seventh micro-element the movable partthe second micro-element is elastically movable by electrostatic forcesbetween the sixth micro-element and the second micro-element and betweenthe seventh micro-element and the second micro-element.
 16. Themicro-electromechanical system according to claim 14, wherein (a) thesubstrate is constructed as a flat extensive solid with a principalsurface, and (b) the micro-elements are constructed as regular prismaticbodies whose base surfaces are aligned parallel to the principalsurface, wherein (c) the movable part of the second micro-element isconstructed as a regular prismatic body and is laterally movable and (d)the base surface of the regular prismatic body forming the movable parteither has the form of a symmetrical antinode in the switch-off positionand has the form of an asymmetric antinode in the switch-on position, ordescribes two parallel cosinusoidal lines which are interconnected atthe centre between their two ends.
 17. The micro-electromechanicalsystem according to claim 1, wherein (a) the substrate is constructed asa flat extensive body with a principal surface and (b) eachmicro-element is constructed as regular prismatic bodies whose basesurfaces are aligned parallel to the principal surface, wherein (c)there is at least one micro-element bistably switchable between aninitial position and a working position, whose switch section contains afirst fixed end fixedly connected to the substrate, a second fixed endfixedly connected to the substrate and a movable part arranged betweenthese two fixed ends, (d) which movable part is constructed as a regularprismatic body and is laterally movable and (e) the base surface of theregular prismatic body forming the movable part either has the form of asymmetrical antinode in the switch-off position and has the form of anasymmetric antinode in the switch-on position, or describes two parallelcosinusoidal lines which are interconnected at the centre between theirtwo ends.
 18. The micro-electromechanical system according to claim 3,wherein the movable part of the second micro-element is elasticallydeformable from the initial position A to the working position A byswitching the first micro-element.
 19. The micro-electromechanicalsystem according to claim 18, wherein (a) the micro-electromechanicalsystem has two fixed contacts fixedly connected to the substrate and (b)that the movable part of the second micro-element has an electricallyconductive contact region, which contact region is arranged in the areaof an end of the second micro-element opposite to the first fixed end ofthe second micro-element and through which contact region in theswitch-off position of the second-microelement the two fixed contactsare interconnected in a conducting fashion.
 20. Themicro-electromechanical system according to claim 1, wherein (a) thesubstrate is constructed as a flat extensive body with a principalsurface, characterised in (b) the switch section of the firstmicro-element is horizontally movable and (c) the movable part of thesecond micro-element is horizontally movable.
 21. A method formanufacturing a micro-electromechanical system in which method (a) afirst micro-element connected to the substrate is produced from asubstrate and (b) a second micro-element connected to the substrate isproduced from a substrate, and (c) using a structuring method, a firstface of the first micro-element and a second face of the secondmicro-element are formed which faces face one another and are at adistance from one another, wherein (d) the first micro-element is formedsuch that it is located in an initial position, it is bistablyswitchable from the initial position into a working position and thedistance of the first face from the second face in the working positionis smaller that a minimal distance producible by the structuring methodbetween the first face and the second face and (e) after forming thefirst face and the second face by the structuring method, the firstmicro-element is switched into the working position.
 22. The method ofmanufacture according to claim 21, wherein before switching the firstmicro-element into the working position, the first face of the firstmicro-element is provided with a first electrically conducting orelectrically non-conducting coating, and/or the second face of thesecond micro-element is provided with a second electrically conductingor electrically non-conducting coating.
 23. The method of manufactureaccording to claim 21, wherein a resulting micro-electro mechanismsystem comprises a substrate as well as a first micro-element and asecond micro-element, wherein (a) the first micro-element and the secondmicro-element are connected to the substrate and (b) the firstmicro-element has a first face and the second micro-element has a secondface, which faces face one another and are produced by a structuringmethod, wherein (d) the first micro-element contains a switch section bywhich it is bistably switchable between an initial position and aworking position, and (e) the distance between the first face and thesecond surface in the working position of the first micro-element issmaller than a minimal distance producible by the structuring methodbetween the first face and the second face.